Recently, due to the demand of making the element compact, the semiconductor chip is demanded to be thinner. The semiconductor chip is ground to the predetermined thickness by the back side grinding after the circuit is formed on the front surface. Therefore, in order to make the element compact, the wafer must be ground further thinner by the back side grinding. However, along with the thickness of the wafer becomes thinner, the wafer strength declines, and the wafer may break even by a small impact. As a cause of the wafer break, “a fractured layer” is thought to be the main cause which is the mixture of the grinding scars of the grinder used during the back side grinding or an oxidized layer or so.
The fractured layer is a minute roughness of the wafer surface which has been ground, and it is under the condition that a polycrystalline of silicon or a silicon which has been oxidized by small amount of the oxygen, further the lattice defect are thought to be included. Due to the stress caused by the roughness or the compositional changes of the surface, a crack may occur even by a small impact and cause the wafer break. Thus, after the back side grinding is completed, in order to remove the fractured layer, it has been generalized to carry out the chemical etching or plasma etching or so to the back side. By removing the fractured layers, the wafer strength is improved, and a good handling property is maintained even for the wafer which has been ground extremely thin.
However, by removing the fractured layer, the deterioration of the contamination resistance property of the obtained wafer or chip against metals is concerned.
The semiconductor wafer contacts with various members when forming the circuit or during the back side grinding and the mounting or so. At this time, a metal such as copper or so is released from these other members, and the wafer may be contaminated by the metals. The metal impurities accumulates in the wafer, and it may be ionized under the heat applying condition such as reflow or so and may move inside the wafer. Then, the metal which has reached the circuit surface interfere the electrical operation of the product and causes a malfunction. Also, metal ion which has reached the circuit surface may generate a metal at the circuit face (these may be called as migration). Particularly, when the metal is generated on the semiconductor wafer surface in which the wiring is very minute, the short circuit may happen on the circuit, and the yield of the product may decline.
On the other hand, as described in the above, the fractured layer is a minute roughness and it is under the condition that a polycrystalline of silicon or silicon which has been oxidized by small amount of the oxygen, and further the lattice defect are thought to be included, thus due to these composition and the unevenness of the structures, said metal impurities are easily captured, thereby it is thought that the influence of the metal impurities may be reduced. The function of such fractured layer is also called as the gettering function.
As such, by removing the fractured layer after the back side grinding of the wafer, the strength of the wafer may be improved however the gettering function is interfered, and the product yield declines. Thus, the techniques is proposed to provide a gettering function by carrying out a various treatment to the semiconductor wafer or chip after the removal of the fractured layer (Patent Articles 1 and 2).